1. Field of the Invention
This disclosure relates to methods for manufacturing a filled gap region or cavity between two surfaces, as for example, an underfill in flip-chip packages, die attachments or die stacks.
2. Description of Related Art
In modern electronic devices, substantial gains in performance are continuously achieved by means of circuit miniaturization and by the integration of single-package multi-functional chips. The scalability and performance of such electronic devices are related to their ability to dissipate heat. In typical flip-chip arrangements, one integrated circuit (IC) surface is used for heat removal through a heat sink, while the other for power delivery and data communication. Power is delivered throughout solder balls attached to electrical pads on the IC chip that are reflowed and coupled to the main circuit board.
To minimize mechanical stress in the solder balls and to protect them electrically, mechanically, and chemically, the gap region between an IC chip and board, created due to the presence of solder balls, is conventionally filled with electrically non-conductive materials known as underfills. Current efforts towards 3D chip integration, with solder balls as electrical connection between silicon dies, demand high thermally conductive underfills to efficiently dissipate the heat of lower dies to the heat removal embodiment attached at the chip stack backside. Some flip-chip on-board applications do also benefit from efficient heat dissipation from the semiconductor die into the board. Hence, thermal underfills between semiconductor and board are desirable. Additionally, electric joints between circuit board pads and metallic coatings at chips should be flexibly produced.
Conventional thermal underfills may consist of a curable matrix (e.g. epoxy resin) loaded with silica fillers, which have a similar thermal expansion coefficient (CTE) to that of the silicon. Currently, the requirement of matching CTE with the solder balls dictates the type, and volumetric fill of fillers to be employed in a given underfill. For thermal underfills the thermal conductivity of filler materials which are used to increase the thermal contact and enhance heat dissipation between connected surfaces should be high. Therefore, Al2O3, AlN, BN or other metal and nonmetal materials are used.
Conventionally, an underfill material can be dispensed into a gap between chips or a flip-chip and a substrate by injecting the filling material along the lateral sides of the gap. U.S. Pat. No. 6,214,635 describes a method and an apparatus for underfilling the gap between a semiconductor device and a substrate by inclining the substrate and semiconductor and introducing filling material along a side wall or through one central hole in the substrate. The underfill then flows into the gap and forms an underfill.